The present invention is related to reactors, systems with reaction chambers, and methods for depositing materials used in the manufacturing of micro-devices.
Thin film deposition techniques are widely used in the manufacturing of micro-devices to form a coating on a workpiece that closely conforms to the surface topography. The size of the individual components in the devices is constantly decreasing, and the number of layers in the devices is increasing. As a result, the density of components and the aspect ratios of depressions (e.g., the ratio of the depth to the size of the opening) are increasing. The size of workpieces is also increasing to provide more real estate for forming more dies (i.e., chips) on a single workpiece. Many fabricators, for example, are transitioning from 200 mm to 300 mm workpieces, and even larger workpieces will likely be used in the future. Thin film deposition techniques accordingly strive to produce highly uniform conformal layers that cover the sidewalls, bottoms, and corners in deep depressions that have very small openings.
One widely used thin film deposition technique is Chemical Vapor Deposition (CVD). In a CVD system, one or more precursors that are capable of reacting to form a solid thin film are mixed in a gas or vapor state, and then the precursor mixture is presented to the surface of the workpiece. The surface of the workpiece catalyzes the reaction between the precursors to form a solid thin film at the workpiece surface. A common way to catalyze the reaction at the surface of the workpiece is to heat the workpiece to a temperature that causes the reaction.
Although CVD techniques are useful in many applications, they also have several drawbacks. For example, if the precursors are not highly reactive, then a high workpiece temperature is needed to achieve a reasonable deposition rate.
Such high temperatures are not typically desirable because heating the workpiece can be detrimental to the structures and other materials already formed on the workpiece. Implanted or doped materials, for example, can migrate within the substrate at higher temperatures. On the other hand, if more reactive precursors are used so that the workpiece temperature can be lower, then reactions may occur prematurely in the gas phase before reaching the substrate.
This is undesirable because the film quality and uniformity may suffer, and also because it limits the types of precursors that can be used.
Atomic Layer Deposition (ALD) is another thin film deposition technique. FIGS. 1A and 1B schematically illustrate the basic operation of ALD processes. Referring to FIG. 1A, a layer of gas molecules Ax coats the surface of a workpiece W. The layer of Ax molecules is formed by exposing the workpiece W to a precursor gas containing Ax molecules, and then purging the chamber with a purge gas to remove excess Ax molecules. This process can form a monolayer of Ax molecules on the surface of the workpiece W because the Ax molecules at the surface are held in place during the purge cycle by physical adsorption forces at moderate temperatures or chemisorption forces at higher temperatures. The layer of Ax molecules is then exposed to another precursor gas containing By molecules. The Ax molecules react with the By molecules to form an extremely thin layer of solid material on the workpiece W. The chamber is then purged again with a purge gas to remove excess By molecules.
FIG. 2 illustrates the stages of one cycle for forming a thin solid layer using ALD techniques. A typical cycle includes (a) exposing the workpiece to the first precursor Ax, (b) purging excess Ax molecules, (c) exposing the workpiece to the second precursor By, and then (d) purging excess By molecules. In actual processing, several cycles are repeated to build a thin film on a workpiece having the desired thickness. For example, each cycle may form a layer having a thickness of approximately 0.5-1.0 xc3x85, and thus it takes approximately 60-120 cycles to form a solid layer having a thickness of approximately 60 xc3x85.
FIG. 3 schematically illustrates an ALD reactor 10 having a reaction chamber 20 coupled to a gas supply 30 and a vacuum 40. The reactor 10 also includes a heater 50 that supports the workpiece W and a gas dispenser 60 in the reaction chamber 20. The gas dispenser 60 includes a plenum 62 operatively coupled to the gas supply 30 and a distributor plate 70 having a plurality of holes 72. In operation, the heater 50 heats the workpiece W to a desired temperature, and the gas supply 30 selectively injects the first precursor Ax, the purge gas, and the second precursor By as shown above in FIG. 2. The vacuum 40 maintains a negative pressure in the chamber to draw the gases from the gas dispenser 60 across the workpiece W and then through an outlet of the reaction chamber 20.
One drawback of ALD processing is that it has a relatively low throughput compared to CVD techniques. For example, ALD processing typically takes about eight to eleven seconds to perform each Ax-purge-By-purge cycle. This results in a total process time of approximately eight to eleven minutes to form a single thin layer of only 60 xc3x85. In contrast to ALD processing, CVD techniques only require about one minute to form a 60 xc3x85 thick layer. The low throughput of existing ALD techniques limits the utility of the technology in its current state because ALD may be a bottleneck in the overall manufacturing process.
Another drawback of both CVD and ALD processing is that it is difficult to deposit the precursors uniformly across the workpiece. For example, typical conventional reactors flow the precursors either (a) laterally across the workpiece (not shown) or (b) vertically downward onto a center region of the workpiece and then radially outward across a perimeter region of the workpiece (FIG. 3). The conventional reactors deposit more material on the portion of the workpiece proximate to the gas inlets than the portion of the workpiece proximate to the outlets because the precursors are depleted as they flow over the workpiece. For example, the reactor that flows the precursors downward and then radially outward deposits more material at the center of the workpiece than at the perimeter of the workpiece. Accordingly, there is a need to improve the process of depositing materials in reactors.
The present invention relates to reactors, systems with reaction chambers, and methods for depositing materials used in the manufacturing of micro-devices. One aspect of the invention is directed to a method for depositing material onto a micro-device workpiece in a reaction chamber. In one embodiment, the method includes flowing a first gas along a first vector across a first portion and toward a center of the micro-device workpiece and flowing a second gas along a second vector across a second portion and toward the center of the micro-device workpiece. The second vector is transverse to the first vector. In one aspect of this embodiment, the method further includes exhausting the first gas from a region proximate to the center of the micro-device workpiece and exhausting the second gas from the region proximate to the center of the micro-device workpiece. In another aspect of this embodiment, flowing the first gas includes depositing a first thickness of the first gas molecules onto the micro-device workpiece proximate to a perimeter and depositing a second thickness of the first gas molecules onto the micro-device workpiece proximate to the center. The first thickness is generally equal to the second thickness.
In another embodiment, the method includes flowing a gas across a surface of the micro-device workpiece from a perimeter region toward a center region and exhausting the gas from the center region of the micro-device workpiece. In one aspect of this embodiment, flowing the gas includes uniformly depositing the gas across a first area from a perimeter to a center of the microdevice workpiece. In another aspect of this embodiment, flowing the gas includes decreasing the density of the gas as the gas moves toward the center of the micro-device workpiece. In another aspect of this embodiment, flowing the gas includes flowing a first precursor. The method can further include flowing a second precursor across and toward the center of the micro-device workpiece at least partially simultaneously with the first precursor flow. Alternatively, the method can further include flowing a purge gas toward the center of the micro-device workpiece after terminating the first precursor flow and flowing a second precursor after terminating the purge gas flow.
Another aspect of the invention is directed to a reactor for depositing material onto a micro-device workpiece in a reaction chamber. In one embodiment, the reactor includes a reaction chamber and a gas distributor carried by the reaction chamber. The gas distributor includes a first aperture arranged to flow a first gas across a first portion and toward a center of the micro-device workpiece and a second aperture arranged to flow a second gas across a second portion and toward the center of the micro-device workpiece. The first portion of the micro-device workpiece is different than the second portion. In one aspect of this embodiment, the reactor further includes an exhaust conduit coupled to the reaction chamber. The exhaust conduit has a port proximate to a center of the micro-device workpiece to remove the first and second gases from the reaction chamber.